1. Field of the Invention
The present invention relates to optical information recording and reading apparatus for recording and/or reading information at a high density by using a near-field light-generating device as a near-field optical head, the device having a minute aperture for producing near-field light.
2. Description of the Related Art
Information recording apparatus using light is evolving toward greater capacities and smaller sizes. Therefore, recording capacities are required to achieve higher densities. As a countermeasure against it, research using a blue-violet semiconductor laser has been conducted. With these techniques, however, an improvement that is only several times of the present recording density can be expected because of the problem of light diffraction limit. In contrast with this, information recording/reading method using near-field light is expected as a technique for treating optical information about a minute area exceeding the light diffraction limit. Today, near-field optical probes permitting optical observation of samples or the like have been put into practical use using the near-field light. Furthermore, using near-field optical heads in information recording apparatus has been discussed.
In this technique, near-field light produced near an optical aperture is utilized, the aperture having a size of less than the light wavelength and formed in a near-field optical head that is a near-field light-generating device. This makes it possible to treat optical information in a region of less than light wavelength that was regarded as a limit for conventional optics. A method of reading optical information can be either collection mode method, in which light is shone onto the surface of a recording medium to produce interaction between near-field light localized around a minute mark and a minute aperture for conversion into scattering light, or illumination mode method in which near-field light produced by a minute aperture is shone onto the surface of a recording medium and scattering light is detected by a separate light-receiving device, the scattering light being converted by interaction with the surface of the recording medium on which information has been recorded by microscopic unevenness or variations in an optical constant such as refractive index. Recording is made by directing near-field light produced by a minute aperture onto the surface of a recording medium and varying the shape of a microscopic area on the medium (heat mode recording) or by varying the refractive index or transmissivity of the microscopic area (photon mode recording). Higher density exceeding those achieved by the prior art information recording apparatus is accomplished by using a near-field optical head having an optical minute aperture exceeding the light diffraction limit.
Under these circumstances, information recording apparatus employing near-field light is generally identical in configuration with magnetic drives and uses a near-field optical head instead of a magnetic head. The near-field optical head has an optical minute aperture and is attached to the front end of a suspension arm. This head is made to float at a given height by making use of pneumatic lubrication, and access to arbitrary data existing on the disk is gained. To cause the near-field optical head to follow the disk rotating at a high speed, a function of stabilizing the posture according to waviness of the disk is given.
In the near-field optical head of this structure, the adopted method of supplying light to the aperture consists of connecting optical fiber or optical waveguide with the near-field optical head and directing light coming from a light source into a minute aperture formed in the near-field optical head.
In this information recording apparatus, light flux having some spread and shone from the end surface of the optical waveguide is reflected by a mirror or the like and directed into the minute aperture. Therefore, the energy density of the light near the minute aperture decreases. This reduces the intensity of near-field light produced from the minute aperture.
Accordingly, a lens is mounted between the end surface of the optical waveguide and the minute aperture. The light flux shone from the end surface of the optical waveguide is collected to the vicinities of the minute aperture by a lens, intensifying the near-field light produced from the minute aperture. Thus, the efficiency of utilization of the light is enhanced. The focused light spot is narrowed by using a lens with a high NA. The light energy can be concentrated to a smaller area. The intensity of the near-field light produced near the minute aperture can be increased by placing the minute aperture at this focal spot. The light flux from the light source can be utilized efficiently.
The above-described information recording apparatus is made up of a large number of components including the optical waveguide and mirror. The number of adjusted parts is also increased. Consequently, the cost is increased due to deteriorated performance and prolonged adjustment time.
Accordingly, in Japanese patent laid-open No. 2000-215494, a flexible rodlike optical waveguide is used, and a reflective surface for reflecting at least a part of light propagating within a core on a clad is formed at the side of one end of the optical waveguide. A light-shielding film for blocking transmission of light is formed on the surface of the clad around the portion through which the light reflected by the reflective surface is transmitted. A part of the light-shielding film is cut away to form an aperture portion smaller than the wavelength of the used light. Near-field light is produced from this aperture portion to thereby realize a cantilevered pickup. Thus, optical information recording apparatus of quite simple structure is offered.
The information recording apparatus fabricated by preparing optical waveguide, mirror, lenses, and so on separately and assembling them is required to efficiently guide light flux from a light source to a minute aperture formed in a near-field optical head in order to produce the sufficiently strong near-field light from the minute aperture and to realize recording and reading of ultrahigh-density information, as well as high S/N. Therefore, the optical waveguide (e.g., thin-film optical waveguide, optical fiber, or the like), mirror, and lenses are necessary. This increases the number of components, which in turn increases the number of locations to be adjusted. This leads to increase the cost. Furthermore, the added components increase the weight of the near-field optical head. Where the head is made to perform a seek operation at a high speed, residual vibration increases. This makes it difficult to record and read information at a high speed.
In the information recording apparatus using the optical pickup of Japanese patent laid-open No. 2000-215494, light flux propagating inside the core of the optical waveguide is reflected by the reflective surface toward the direction in which the light passes through the clad, and thus the flux is guided to the minute aperture. Therefore, the reflected light flux has an angle of spread and is guided to the minute aperture while dispersing. Therefore, the energy density of light flux in the minute aperture drops, making it impossible to create sufficiently strong near-field light near the minute aperture. Accordingly, attempts are made to increase the energy density of the light flux guided to the minute aperture. In particular, a quite small ball lens is inserted between the minute aperture and the core on which the reflective surface is formed in order to increase the NA of the light flux entering the minute aperture and to increase the energy density of the light flux at the minute aperture.
The NA of the light flux entering the minute aperture can be increased by increasing the diameter of the light flux incident on the lens and using a lens having a short focal distance. To increase the diameter of the light flux incident on the lens, it is necessary to set the distance from the core end surface to the lens to a sufficiently large value.
However, a rodlike optical waveguide having flexibility normally has a thickness of less than about 100 xcexcm and therefore it is difficult to increase the NA in order to increase the energy density of the light flux entering the minute aperture. Although the NA of the light flux entering the minute aperture can be increased by increasing the thickness of the optical waveguide and increasing the distance between the core on which the reflective surface is formed and the ball lens, the flexibility of the optical waveguide is deteriorated. Furthermore, the optical pickup is thickened, elevating the position of the center of gravity. This makes it difficult to perform high-speed tracking.
It is an aspect of the present invention to provide inexpensive information recording apparatus which efficiently guides light flux from a light source to a minute aperture, avoids increases in the number of components, reduces the mass of the near-field optical head, produces stronger near-field light near the minute aperture, performs high-speed tracking, records and reads information at an ultrahigh density and at a high speed, and increases the S/N of the read signal.
It is another aspect of the present invention to provide first optical information recording and reading apparatus that makes use of near-field light and comprises: a light source; a near-field optical head; a rodlike optical waveguide for transmitting light from said light source, the waveguide supporting said near-field optical head and having flexibility; a core formed within said optical waveguide; a reflective surface formed in a surface of said optical waveguide opposite to an end surface on the side of said light source, the reflective surface acting to reflect at least a part of light propagating inside said optical waveguide toward said near-field optical head; light-collecting structures for collecting light reflected by said reflective surface; an optical minute aperture portion formed in said near-field optical head; a recording medium; a light-receiving portion; a suspension arm that supports said optical waveguide; and an actuator for moving relative positions of said minute aperture and said recording medium. This apparatus is characterized in that an end surface perpendicular to the direction of propagation of light in said core is formed in an intermediate position of said optical waveguide and located in a part fixed to said near-field optical head.
Therefore, ultrahigh-density recording and reading of information are enabled by using near-field light. In addition, light flux having a high energy density can be collected into the minute aperture in the near-field optical head. Consequently, the strength of the near-field light produced near the minute aperture is increased. This can immensely increase the efficiency of utilization of light. This makes it unnecessary to use a high-power laser. Heat generation from the laser can be suppressed. Hence, lower power consumption and miniaturization of the apparatus are enabled. In this way, optical information recording and reading apparatus capable of increasing the S/N of the read signal and realizing high-speed recording and reading is offered.
Since the reflective surface, core, and optical waveguide can be integrally formed, it is not necessary to align them to each other. The number of components can be reduced. Furthermore, the core end that is the exit end for light is formed in the region bonded to the near-field optical head. Therefore, if the near-field optical head swings relative to the optical waveguide, the relative positions of the reflective surface, core end, and minute aperture do not vary. Consequently, it is easy to guide a given amount of light into the minute aperture.
Therefore, information recording and reading apparatus permitting a further decrease in the cost of the apparatus and stabilization of the intensity of near-field light produced near the minute aperture can be offered.
It is another aspect of the present invention to provide second optical information recording and reading apparatus, wherein the above-described light-collecting structures are lens structures formed in the near-field optical head described above.
It is another aspect of the present invention to provide third optical information recording and reading apparatus, wherein the above-described light-collecting structures are formed in the above-described optical waveguide.
Therefore, the number of components can be reduced further, in addition to the advantages of the first information recording and reading apparatus according to the invention, because the light-collecting structures and the near-field optical head or the light-collecting structure and the optical waveguide can be integrated. This can lead to a further decrease in the size of the apparatus. The apparatus can be fabricated with lower cost.
It is another aspect of the present invention to provide fourth optical information recording and reading apparatus, wherein the above-described optical waveguide is provided with cutouts to form at least one beam supported at its both ends. The near-field optical head is resiliently supported.
Therefore, the advantages of any one of the first through third optical information recording and reading apparatuses according to the invention can be had. In addition, the both end-supported beam structure formed in the optical waveguide is operated as a spring to maintain constant the distance between the minute aperture and the recording medium. In consequence, the number of components can be reduced further. The cost can be curtailed further.
It is another aspect of the present invention to provide fifth optical information recording and reading apparatus, wherein the above-described core is formed within the both end-supported beam structure formed in said optical waveguide.
The advantages of the fourth optical information recording and reading apparatus according to the invention can be had. In addition, the optical waveguide can be formed without sacrificing the light transmission function and the function of maintaining constant the distance between the minute aperture and the recording medium. In consequence, the apparatus can be miniaturized further.